Write individual fortunes on strips of paper. Sift flour, cornstarch, sugar, and salt into a medium bowl. Add oil, egg whites, water, and vanilla extract; stir until smooth. Preheat oven to 300 degrees. Bake 1 cookie at a time. Drop 1/4 cup batter onto an oiled baking sheet; spread evenly to make an 8-inch circle. Bake until cookie turns light golden brown, 12 to 14 minutes. (Don't allow edges to become overly brown or cookie will crack when folded.) Using pot holders to protect your hands, immediately remove hot, pliable cookie from baking sheet and place a fortune in center. Fold cookie in half to form a half-moon, then grasp ends of cookie and gently pull together to crease. Hold folded cookie for a minute to maintain its shape as it cools and becomes crisp. Repeat with remaining batter.